Search Results (174 total)

We report the results of a search for a W^′ boson produced in pp̅ collisions at a center-of-mass energy of 1.8 TeV using a 107 pb^-1 data sample recorded by the Collider Detector at Fermilab. We consider the decay channel W^′→μν_μ and search for anomalous production of high transverse mass μν_μ lepton pairs. We observe no excess of events above background and set limits on the rate of W^′ boson production and decay relative to standard model W boson production and decay using a fit of the transverse mass distribution observed. If we assume standard model strength couplings of the W^′ boson to quark and lepton pairs, we exclude a W^′ boson with invariant mass less than 660 GeV/c² at 95% confidence level.

We report the first direct measurement of bb̅ rapidity correlations in pp̅ collisions at sqrt[s]=1.8 TeV. We select events with a high transverse momentum muon accompanied by a jet, and a second jet associated with a decay vertex displaced from the pp̅ interaction vertex. Two independent samples are obtained corresponding to events with a forward (2.0<|η|<2.6) or central (|η|<0.6) muon. We measure the ratio of forward to central bb̅ production to be 0.361±0.033(stat)_-0.031^+0.015(syst), in good agreement with the next-to-leading order QCD prediction 0.338_-0.097^+0.014.

If the technicolor ω_T particle exists, a likely decay mode is ω_T→γπ_T, followed by π_T→bb̅ , yielding the signature γbb̅ . We have searched 85 pb^-1 of data collected by the CDF experiment at the Fermilab Tevatron for events with a photon and two jets, where one of the jets must contain a secondary vertex implying the presence of a b quark. We find no excess of events above standard model expectations. We express the result as an exclusion region in the M_ωT-M_πT mass plane.

A new technique to measure the ratio of b quark fragmentation fractions in pp̅ collisions is described. Using a 70-pb^-1 sample of low-mass dimuon trigger data recorded with the Collider Detector at Fermilab, we identify B mesons by observing the double semileptonic decays b→cμX with c→sμX. By counting the numbers of K^*(892)⁰, K^*(892)⁺, and φ(1020) mesons produced in association with these muon pairs, we measure the ratio of strange to nonstrange B meson production to be f_s/(f_u+f_d)=[21.0±3.6(stat)_-3.0^+3.8(syst)]%. This measurement is the most precise available from hadron collisions to date. Limits on the branching fractions of semileptonic charm meson decays with K₁(1270), K₁^*(1410), and K₂^*(1430) mesons in the final state are also obtained.

We present the first measurement of associated direct photon+muon production in hadronic collisions, from a sample of 1.8 TeV pp̅ collisions recorded with the Collider Detector at Fermilab. Quantum chromodynamics (QCD) predicts that these events are primarily from the Compton scattering process cg→cγ, with the final state charm quark producing a muon. Hence this measurement is sensitive to the charm quark content of the proton. The measured cross section of 29±9 pb is compared to a leading-order QCD parton shower model as well as a next-to-leading-order QCD calculation.

We present a search for like-sign dielectron plus multijet events using 107 pb^-1 of data in pp̅ collisions at sqrt[s]  =  1.8 TeV collected in 1992–1995 by the CDF experiment. Finding no events that pass our selection, we set σ×BR limits on two supersymmetric processes that can produce this experimental signature: gluino-gluino or squark-antisquark production with R-parity violating decays of the charm squark or lightest neutralino via a nonzero λ₁₂₁^′ coupling. We compare our results to the next-to-leading order calculations for gluino and squark production cross sections and set lower limits on M(g̃), M(t̃₁), and M(q̃).

We present a measurement of the mass difference Δm_d for the B⁰ meson and the statistical power of the b flavor tagging methods used. The measurement uses 90 pb^-1 of data from pp̅ collisions at sqrt[s]=1.8 TeV collected with the CDF detector. An inclusive lepton trigger is used to collect a large sample of B hadron semileptonic decays. The mass difference Δm_d is determined from the proper time dependence of the fraction of B hadrons that undergo flavor oscillations. The flavor at decay is inferred from the charge of the lepton from semileptonic B decay. The initial flavor is inferred by determining the flavor of the other B hadron produced in the collision, either from its semileptonic decay (soft-lepton tag) or from its jet charge. The measurement yields Δm_d=(0.500±0.052±0.043)ħ ps^-1, where the first uncertainty is statistical and the second uncertainty is systematic. The statistical powers (εD²) of the soft-lepton and jet-charge flavor taggers are (0.91±0.10±0.11)% and (0.78±0.12±0.08)%, respectively.

We present a measurement of the mass difference Δm_d of the two B_d⁰ mass eigenstates. We use a flavor tagging method based on the lepton charge, in a sample of events with two muons at low transverse momentum. The sample corresponds to an integrated luminosity of 90 pb^-1 collected by the Collider Detector at Fermilab. The result obtained is Δm_d=0.503±0.064(stat)±0.071(syst) ps^-1.

A search for B_s⁰-B̅ _s⁰ oscillations is performed in a sample of B_s⁰ semileptonic decays collected using dilepton triggers at the Tevatron Collider during 1992–1995. The B_s⁰ is reconstructed using phiv meson-lepton correlations; its initial production flavor is determined with the second lepton in the event. From a signal of 1068 with a B_s⁰ purity of 61%, we obtain a limit on the B_s⁰-B̅ _s⁰ oscillation frequency of Δm_s>5.8 ps^-1 at 95% confidence level.

We report the results of a search for technicolor using 110 pb^-1 of pp̅ collisions recorded by the Collider Detector at Fermilab (CDF). In technicolor models containing a technifamily, color-octet technirhos enhance the pair production of color-triplet technipions, which behave as third-generation leptoquarks. From our previously reported search for third-generation leptoquarks, we present constraints on the production of color-triplet technipions and color-octet technirhos as a function of their masses.

We present a detailed description of a search for anomalous production of missing E_T (E/_T), jets, leptons (e,μ,τ), b quarks, or additional photons in events containing two isolated, central (|η|<1.0) photons with E_T>12 GeV. The results are consistent with standard model expectations, with the possible exception of one event that has, in addition to the two photons, a central electron, a high-E_T electromagnetic cluster, and large E/_T. We set limits using two specific SUSY scenarios for production of diphoton events with E/_T.

The kinematic properties of tt̅ events are studied in the W+multijet channel using data collected with the CDF detector during the 1992–1995 runs at the Fermilab Tevatron collider corresponding to an integrated luminosity of 109 pb^-1. Distributions of a variety of kinematic variables chosen to be sensitive to different aspects of tt̅ production are compared with those expected from Monte Carlo calculations. A sample of 34 events rich in tt̅ pairs is obtained by requiring at least one jet identified by the silicon vertex detector (SVX) as having a displaced vertex consistent with the decay of a b hadron. The data are found to be in good agreement with predictions of the leading order tt̅ matrix element with color coherent parton shower evolution.

We have used 87 pb^-1 of data collected with the collider detector at Fermilab to search for new particles decaying to bb̅ . We present model-independent upper limits on the cross section for narrow resonances which exclude the color-octet technirho in the mass interval 350<M<440 GeV/c². In addition, we exclude top-gluons, predicted in models of top-color-assisted technicolor, of width Γ  =  0.3M in the mass range 280<M<670 GeV/c², of width Γ  =  0.5M in the mass range 340<M<640 GeV/c², and of width Γ  =  0.7M in the mass range 375<M<560 GeV/c².

We present a measurement of Z⁰ boson and Drell-Yan production cross sections in p̅ p collisions at sqrt[s]=1.8 TeV using a sample of 107 pb^-1 accumulated by the Collider Detector at Fermilab. The Drell-Yan cross section is measured in the mass range of M_μμ>40 GeV/c². We compare the measurements with the predictions of quantum chromodynamics in both leading order and next-to-leading order, incorporating the recent parton distribution functions. The measurements are consistent with the standard model expectations.

We present a new measurement of the top quark mass in tt̅ events in which both W bosons from top quarks decay into leptons (eν,μν). We use events collected by the CDF experiment from pp̅ collisions at sqrt[s]  =  1.8 TeV at the Tevatron collider. We measure a top quark mass of 167.4±10.3(stat)±4.8(syst)  GeV/c² from a sample of eight events. We combine this result with previous CDF measurements in other decay channels to obtain a final mass value of 176.0±6.5 GeV/c².

The lifetime of the B_S⁰ meson is measured using the semileptonic decay B_S⁰→D_S^-l⁺νX. The data sample consists of about 110 pb^-1 of pp̅ collisions at sqrt[s]=1.8 TeV collected by the CDF detector at Fermilab. Four different D_S^- decay modes are reconstructed resulting in approximately 600 D_S^-l⁺ signal events. The B_S⁰ meson lifetime is determined to be τ(B_S⁰)=(1.36±0.09_-0.05^+0.06) ps, where the first and second uncertainties are statistical and systematic, respectively. The B_S⁰ meson decay length distribution is examined for a lifetime difference ΔΓ/Γ between the two mass eigenstates of the B_S⁰ meson. An upper limit of ΔΓ/Γ<0.83 is set at the 95% confidence level.

We describe a measurement of the charge asymmetry of leptons from W-boson decays in the rapidity range 0<|y_l|<2.5 using W→eν,μν events from 110±7 pb^-1 of data collected by the CDF detector during 1992–1995. The asymmetry data constrain the ratio of d and u quark momentum distributions in the proton over the x range of 0.006 to 0.34 at Q²≈M_W². The asymmetry predictions that use parton distribution functions obtained from previously published CDF data in the central rapidity region ( 0.0<|y_l|<1.1) do not agree with the new data in the large rapidity region ( |y_l|>1.1).

We search for Higgs bosons produced in association with a massive vector boson in 91±7 pb^-1 of pp̅ collisions at sqrt[s]  =  1.8 TeV recorded by the Collider Detector at Fermilab. We assume the Higgs scalar H⁰ decays to a bb̅ pair with branching ratio β, and we consider the hadronic decays of the vector boson V ( W or Z). Observations are consistent with background expectations. We place 95% confidence level upper limits on σ(pp̅ →H⁰V)β as a function of the scalar mass (M_H⁰) over the range 70<M_H⁰<140 GeV/c². When combined with an analysis of the case where V is a leptonically decaying W, these limits vary from 23 pb at M_H⁰  =  70 GeV/c² to 17 pb at M_H⁰  =  140 GeV/c².

We have searched for the decays B_s⁰→e^±μ^∓ and B_d⁰→e^±μ^∓ using a 102 pb^-1 data sample of pp̅ collisions at sqrt[s]  =  1.8 TeV collected with the Collider Detector at Fermilab. We set upper limits on the branching fractions of B(B_s⁰→e^±μ^∓)<6.1(8.2)×10^-6 and B(B_d⁰→e^±μ^∓)<3.5(4.5)×10^-6 at 90(95)% confidence level. Using these limits, we set lower bounds on the corresponding Pati-Salam leptoquark masses and find that M_LQ(B_s⁰)>20.7(19.3)  TeV/c² and M_LQ(B_d⁰)>21.7(20.4)  TeV/c² at 90(95)% confidence level.

B_d⁰-B_d⁰ oscillations are observed in “self-tagged” samples of partially reconstructed B mesons decaying into a lepton and a charmed meson collected in pp̅ collisions at sqrt[s]=1.8 TeV. A flavor tagging technique is employed which relies upon the correlation between the flavor of B mesons and the charge of a nearby particle. We measure the flavor oscillation frequency to be Δm_d=0.471_-0.068^+0.078±0.034 ps^-1. The tagging method is also demonstrated in exclusive samples of B_u⁺→J/ψK⁺ and B_d⁰→J/ψK^*0(892), where similar flavor-charge correlations are observed. The tagging characteristics of the various samples are compared with each other, and with Monte Carlo simulations.

We present a measurement of the time-dependent asymmetry in the rate for B̅ _d ⁰ versus B_d⁰ decays to J/ψK_S⁰. A nonzero asymmetry would be an indication of CP violation, and within the standard model this may be used to measure the CP-violation parameter sin(2β). A total of 198±17 B_d⁰/B̅ _d ⁰ decays were observed in pp̅ collisions at sqrt[s]  =  1.8 TeV by the CDF detector at the Fermilab Tevatron. B_d⁰ and B̅ _d ⁰ are distinguished by a technique based on charge correlations from hadronization of the b quark. Our analysis results in sin(2β)  =  1.8±1.1(stat)±0.3(syst).

We report a measurement of the fraction of dijet events with a rapidity gap between jets produced by color-singlet exchange in p̅ p collisions at sqrt[s]  =  630 GeV at the Fermilab Tevatron. In events with two jets of transverse energy E_T^jet>8 GeV, pseudorapidity in the range 1.8<|η^jet|<3.5 and η₁η₂<0, the color-singlet exchange fraction is found to be R  =  [2.7±0.7(stat)±0.6(syst)]%. Comparisons are made with results obtained at sqrt[s]  =  1800 GeV and with theoretical expectations.

We report on a search for second generation leptoquarks (Φ₂) using a data sample corresponding to an integrated luminosity of 110 pb ^-1 collected at the Collider Detector at Fermilab. We present upper limits on the production cross section as a function of Φ₂ mass, assuming that the leptoquarks are produced in pairs and decay into a muon and a quark with branching ratio β. Using a next-to-leading order quantum chromodynamics calculation, we extract a lower mass limit of M_Φ2>202(160)  GeV/c² at 95% confidence level for scalar leptoquarks with β  =  1(0.5).

We report the observation of bottom-charmed mesons B_c in 1.8 TeV pp̅ collisions using the CDF detector at the Fermilab Tevatron. The B_c mesons were found through their semileptonic decays, B_c^±→J/ψl^±X. A fit to the J/ψl mass distribution yielded 20.4_-5.5^+6.2 events from B_c mesons. A test of the null hypothesis, i.e., an attempt to fit the data with background alone, was rejected at the level of 4.8 standard deviations. By studying the quality of the fit as a function of the assumed B_c mass, we determined M(B_c)=6.40±0.39 (stat.)±0.13 (syst) GeV/c². From the distribution of trilepton intersection points in the plane transverse to the beam direction we measured the B_c lifetime to be τ(B_c)=0.46_-0.16^+0.18 (stat)±0.03 (syst) ps. We also measured the ratio of production cross section times branching fraction for B_c⁺→J/ψl⁺ν relative to that for B⁺→J/ψK⁺ to be σ(B_c)×B(B_c→J/ψlν) / σ(B)×B(B→J/ψK)=0.132_-0.037^+0.041 (stat)±0.031 (syst)_-0.020^+0.032(lifetime).